Terahertz waves are a segment of electromagnetic waves, which are bounded between millimeter waves (less than 1×1011 Hz) and photonics waves (greater than 1×1013 Hz). The electromagnetic frequencies lower than terahertz band are covering mm waves (microwaves), while the electromagnetic frequencies higher than terahertz band are covering near infrared through visible spectrum.
Terahertz waves band has been used for time and frequency domains imaging. Major applications of terahertz are spectroscopy in atmospheric science and in astronomy, imaging for burn diagnostics, tomography, biomedical, medical diagnostics, screening for weapon, explosives, biohazard, and finally imaging of concealed objects. The discussion of these applications are shown in a book entitled “Sensing with terahertz radiations” edited by D. Mittleman.
Terahertz wave frequencies in the range of 100 to 10000 GHz suffer high insertion losses during wave shaping, multiplexing, and focusing. Current available optics for Terahertz imaging is bulky and designed on refraction principle where in terahertz optics diffractive effects can dominate in ray propagation. Kinoform optics is based on diffraction and support system miniaturization, which in most cases is the only solution for development of portable systems.
One of the problems with the current systems is the optical components that have low efficiency. As a result, the weight of the system is too great for many practical applications. One more deficiency in the prior art is their inability to be packed with 100 percent fill factor. This disadvantage is noticeable when terahertz imaging requires a lens array.